Power systems are going through a paradigm change. At the moment, the frequency of a power system is controlled by regulating a small number of large synchronous generators and most loads do not take part in the frequency control of the system. But now, the landscape of power systems is rapidly changing. Various non-synchronous distributed energy resources (DER), including renewables, electric vehicles and energy storage systems, are being connected to power systems. Moreover, most loads that do not take part in frequency control now are expected to take part in frequency control in the future. Hence, the number of active players to take part in frequency control in the future could easily reach millions, which imposes unprecedented challenges to the frequency stability of future power systems. The fundamental challenge behind this paradigm change is that future power systems will be power electronics-based, instead of electric machines-based, with millions of relatively small, non-synchronous and incompatible players. For example, on the supply side, most DERs are connected to power systems through power electronic converters. In transmission and distribution networks, many power electronic converters, such as HVDC links and FACTS devices, are being introduced to electronically control power systems in order to improve efficiency and controllability. On the load side, most loads will be connected to the grid through power electronic converters as well. For example, motors, which consume over 50% of electricity, are much more efficient when equipped with motor drives; Internet devices, which consume over 10% of electricity, have front-end power electronic converters; lighting devices, which consume about 20% of electricity, are being replaced with LED lights, which have front-end power electronic converters as well. The conventional way of controlling the current of these power electronic converters is no longer appropriate.
It has been shown that power electronic converters can be operated as virtual synchronous machines (VSM) to have the synchronization mechanism of conventional synchronous machines (SM). For example, the synchronverter or the static synchronous generator disclosed in US 2011/0270463 Al directly embeds the mathematical model of SM including the swing equation into the controller of a power electronic converter to control the voltage generated. CN 108667080A discloses a VSM with an inner-loop controller to reduce double-frequency power pulsation under unbalanced grid voltage. The core of these controllers is the swing equation of SM.